1. Technical Field of the Invention
The present invention relates to a component mounting tool, and component mounting method and apparatus using this component mounting tool, wherein a component is mounted on an object by friction-bonding their respective metallic interconnects. In particular, it describes the process of manufacturing an electronic circuit substrate wherein an electronic component such as bare IC chip is mounted onto a printed wiring circuit board in electrical connection therewith by ultrasonic bonding.
2. Description of Prior Art
Bare IC chips are formed of a semiconductor wafer on which circuit patterns are fabricated using thin-film forming techniques and mounted on a printed board thereby manufacturing an electronic circuit board. For electrically connecting electrodes prefabricated with circuit pattern on bare IC chips with conductive lands formed on printed wiring boards, a so-called surface mount method is used wherein the bonding face of an unpackaged IC chip and the bonding face of a board are faced to each other and fixedly mounted so that electrical connection between electrode of chip and conductive land of board is achieved.
The applicants of the present invention have proposed a method of mounting a bare IC chip on a circuit board by ultrasonic-bonding a bump on the chip and a conductive land on the circuit board. More specifically, the bare IC chip, on which a metal bump has been preliminarily formed by a wire bonding process or the like, is held by suction with a suction nozzle and is brought opposite to the circuit board at a predetermined location, where the bump contacts the conductive land. The suction nozzle is rockably supported and ultrasonic vibration is applied to between the support point of the nozzle and working face of nozzle to vibrate the IC chip thereby generating friction between bump and land.
The requirements of secure electrical connection and high mounting strength are satisfied by the above bonding method which involves metal welding. Moreover, chips can be swiftly installed on circuit boards. The suction nozzle is advantageously made of stainless steel as it provides good vibration characteristics and thus suitable for bonding metal interconnects of the chip and board by ultrasonic. However, suction nozzles of stainless steel have a relatively short operational life. This is because the flat working face of suction nozzle having a surface roughness of 3-5 μm becomes soon worn off by friction with chips generated by ultrasonic vibration and is decreased in surface regularity and flatness. Also attributable to such abrasive wear are electrochemical reaction between stainless steel and gallium arsenide or silicone of chips, or foreign matter entering between the working face of nozzle and IC chips. Especially in a case where the component to be bonded is an SAW filter, the working face of suction nozzle becomes easily roughened by hard LiTaO3, LiNbO3, or quartz normally used for SAW filter.
A countermeasure for the above problem is the use of stainless steel having high hardness such as SUS420J2 according to Japanese Industrial Standard which is further hardened by quenching. Even so, after repeating bonding operation about 500 times, bonding failure starts to occur, where IC chips crack or fail to be bonded with required shear strength. When an operator judges in the light of such bonding failure that the current suction nozzle is no longer capable of performing favorable ultrasonic bonding, such nozzle is dismounted from the apparatus and refined with abrasives and reused.
Such maintenance operation which is needed frequently is not only troublesome but also badly affects productivity. Moreover, frequent refining of suction nozzles using abrasives result in shorter operational life of nozzle. By way of example, the suction nozzle is decreased in length to a usable limit after thirty times refining, and normally one nozzle is consumed per month.
The use of a material having superior abrasive wear resistance for the suction nozzle would not solve the problem either, since the vibration characteristics would be deteriorated and ultrasonic bonding itself could not be performed favorably.